The present invention relates to a device for driving a self-piercing rivet into a plurality of components to be fastened, and more particularly to an improved die from such a device.
Self-piercing rivets are frequently used to fasten together aluminum body panels that are unfit for welding. Automotive panels are increasingly being made of aluminum to reduce the overall weight of automobiles, and demand for self-piercing rivets is growing.
An example of a self-piercing rivet fastening device is described in U.S. Pat. No. 5,752,305 issued May 19, 1998, corresponding to Japanese Examined Patent Application Publication No. 8-505087 (Patent Document 1). FIG. 1 and FIG. 2 are drawings of the self-piercing rivet fastening device described in Patent Document 1, and of a self-piercing rivet fastening two components together. As shown in FIG. 1, the two components 5, 6 are clamped with strong force (see the arrows) by the die 2 and nose 3 of the self-piercing rivet fastening device 1, and the self-piercing rivet 9 is driven into the components 5, 6 by the punch 7. The self-piercing rivet 9 has a large-diameter head 10 and tubular legs 11 below the head 10. The components 5, 6 are clamped on the die 2, and the self-piercing rivet 9 is driven into the components 5, 6 by the punch 7.
As shown in FIG. 2, when the self-piercing rivet 9 is properly driven into the components 5, 6, the legs 11 pierce the components 5, 6 and are deformed so that the tips 13 of the legs 11 spread outward, but do not break through the component 6 adjacent to the die 2. The components 5, 6 are thus connected together by the spread legs 11 inside the component 6 and by head 10 of the rivet.
When self-piercing rivets pierce the component 5 adjacent to the punch and pierce, but do not break through, the component 6 adjacent to the die 2, rivet-pierced holes are not formed in the surface of the component 6. Therefore, the sealing properties of the component 6 are not damaged, and the external appearance of the component remains unmarred. However, the legs on the self-piercing rivets may break through the component adjacent to the die and open small holes if that component is not sufficiently thick (e.g., insufficient plate thickness of an automotive body panel).